In the prior art are known both dual-clutch transmissions and transmissions having only one starting and gear clutch which are in countershaft design. In the last mentioned transmission, paraxially with a transmission input shaft connected with the output side of the starting and gear clutch, one countershaft is situated upon which idler and fixed gears are rotatably supported or fastened. At the same time, the idler and fixed gears are in tooth contact with each other forming by pairs one reduction step.
To carry out a concrete ratio change operation, the idler gears can be decelerated with the aid of synchronization means to the rotational speed of the shaft upon which they are supported. Besides, with the idler gears coupling means are coordinated which are disposed non-rotatably and axially displaceably upon the respective transmission shaft. During a concrete gear shift operation with rotational speed uniformity, the coupling means non-rotatably connect the gear specific idler gear with the transmission shaft concerned. The synchronization and coupling means are, in addition, combined to form units with which preferably each two adjacent idler gears can be shifted. The units are also known as shifting sets.
The idler gears of said gear wheel pairs accordingly drive the countershaft alternatively to each other. This countershaft has available for the output one driven gear wheel non-rotatably connected therewith. The driven gear wheel is for its part in tooth contact with a fixed gear upon one output shaft with which can be driven at least one differential transmission of a vehicle drive train.
Especially in multi-ratio transmission, it is advantageous to support the transmission input shaft and the countershaft not only by their respective axial ends by means of roller bearings, but also to situate an additional central bearing approximately in the center of said shafts.
In such a transmission known from the not pre-published DE 102 53 259.1, the driven gear wheel can be fastened upon the countershaft either in a gear wheel group between the roller bearings close to the clutch and the central bearing or in a gear wheel group between the central bearing and the roller bearings removed from the clutch.
In vehicle transmissions, gear wheels designed as helical-cut spur gears are preferred, since they have, in comparison with straight-cut gear wheels, a smoother run and low noise formation. The disadvantage of helical-cut gear wheels is that their toothing forces exert an axial thrust upon the respective transmission shaft and produce bending torques related thereto.
At this point, the invention establishes that the problem to be solved is to introduce a generic transmission with helical-cut transmission gear wheels and low shaft deflection.